Alkyds in organic solvent medium, also referred to as being solvent-based, are resins that have been known for a long time to those skilled in the art, and are used in general in decorative and industrial paint formulations and coatings. To satisfy questions as regards comfort of use, odor and toxicity, specific alkyd emulsions have been developed and marketed for about 20 years, with advantageous performance levels in terms of gloss, drying, appearance/color, stability and odor. A technical solution for conventional implementation, employed to form alkyd emulsions that are stable over time, consists in using a combination of a nonionic surfactant with an anionic surfactant as described in WO 2008/076360.
Despite these improvements, certain parameters and performance levels still remain to be improved, such as the resistance to yellowing, the blocking resistance, the hardness, the water sensitivity and the biodegradability. The tendency toward yellowing is a natural and intrinsic property of alkyd resins, which thus limits their use to quite specific end uses, for instance primers, surface coatings, woods and trims. The first alkyd emulsions described in the literature concern alkyds with large oil lengths of about 65% to 82% as described in Colloids Surfaces A. Physicochem. Eng. Aspects 1995, 94, 161-171. The emulsification of resins with a smaller oil length is relatively difficult to perform, due to the lower affinity of surfactants with the resin, as explained in Prog. Org. Coat. 1994, 24, 281-97. Nevertheless, nowadays, commercial products have an average oil length of 50%, as described in WO 2009/140192 or even a smaller oil length up to approximately 40% for the lowest oil lengths, as described in Prog. Org. Coat. 2000, 40, 253-266 or even more recently in WO 2008/076360. For a more systematic and universal use, it is necessary to find solutions that guarantee products which develop less yellowing for applications of wider scope such as on walls or ceilings. Nowadays, these applications are almost exclusively reserved for acrylic emulsions, which have been known for a long time for their good resistance to yellowing and to oxidation, but acrylic emulsions have drawbacks such as lower gloss, water sensitivity (lower water resistance) and poorer chemical resistance.
The resin of the present invention proposes to overcome the mentioned drawbacks of the prior art, while at the same time affording high dispersibility in water without any need for organic solvent and in the absence of groups that make the resin self-dispersing. This capacity makes it possible to obtain resin dispersions without any organic solvent or protective colloids and which are stable on storage, and to obtain coatings associated with high gloss and high hardness, and, by virtue of its hydrophobic nature, high water resistance, such as high resistance to yellowing over time. An additional advantage during the drying of the resin dispersions according to the present invention is the faster development over time of high, stable hardness, this being achieved without the need for systematic addition of a siccativating agent of cobalt type. This therefore leads to an amicable solution for man and for his environment due to the absence of organic solvents in the dispersion and also the absence of siccativating agents on drying, but also via the choice of the essential raw materials, insofar as a large proportion of these raw materials is of renewable and durable origin and may also lead to chemical structures that are more readily biodegradable. The dispersions of the invention and the coatings resulting therefrom are thus favorable toward environmental protection, while at the same time having application qualities that are at the very least identical, if not improved, with respect to conventional water-based coatings. In addition to the environmental protection, the highly renewable nature of said aqueous binders according to the present invention should be underlined, which binders are predominantly prepared from rosin and natural fatty substances. This advantage is appreciable since, in certain cases, the proportion of renewable raw materials reaches a level of 100% on the overall composition of the resin (surfactants excluded). This enables the manufacture of this novel type of resin, which may be used as binder, by virtue especially of the durable and seasonal availability of said raw materials. These same reasons also make it possible to limit the environmental impact via a reduced carbon imprint and an improved life cycle. These two parameters reflect the impact of the manufactured products on the environment and health. “Renewable” or “bio-sourced” resources in particular make it possible to reduce the emissions of greenhouse gases such as carbon dioxide.